Caprolactam preferred catalyst

The alkaline catalyst systems used for caprolactam polymerization are suitable for both the prepolymer and copolymerization reactions. The preferred catalyst Is caprolactam magnesium bromide, prepared by reaction of Grignard reagent with caprolactam. With NYRIM copolymers, a two-package system Is used—reactive prepolymer and catalyst concentrate. These are dissolved in caprolactam to make up the two reactive streams. 

Ammonolysis is the preferred route currently in use at the DuPont Company for the depolymerization of nylon-6,6 carpet waste. McKinney13 has described the reaction of nylon-6,6 and nylon-6 mixtures with ammonia at temperatures in the range of 300-350°C at a pressure of about 68 atm in the presence of an ammonium phosphate catalyst to form a mixture of nylon-6,6 and nylon-6 monomers (HMD A, A A, and s-caprolactam) and adiponitrile, 5-cyanovaleramide, 6-aminocapronitrile, and 6-aminocaproamide. 

Important solvolysis reactions for nylons are hydrolysis, methanolysis, glycolysis, aminolysis, ammonolysis, transamidation, and acidolysis.17 Hydrolysis of nylon-6 with steam in the presence of an acid catalyst to form caprolactam is tlie preferred depolymerization approach. However, when recycling carpet face fibers, file fillers in the polymer may react with file acid catalyst and lower the efficiency of the catalyst. 

Rhodium carboxylates have been found to be effective catalysts for intramolecular C—H insertion reactions of a-diazo ketones and esters.215 In flexible systems, five-membered rings are formed in preference to six-membered ones. Insertion into methine hydrogen is preferred to a methylene hydrogen. Intramolecular insertion can be competitive with intramolecular addition. Product ratios can to some extent be controlled by the specific rhodium catalyst that is used.216 In the example shown, insertion is the exclusive reaction with Rh2(02CC4F9)4, whereas only addition occurs with Rh2(caprolactamate)4, which indicates that the more electrophilic carbenoids favor insertion. 

Most of the work reported in the literature employs sodium lactamate salt as catalyst and isocyanate/lactam adducts as initiator. Gabbert and Hedrick [14] preferred to work with acyllactam as the initiator and Grignard salts of caprolactam as the catalyst in view of their ease of handling and fewer side reactions compared with the sodium lactamate and isocyanate system. 

Castings of nylon 6 are commonly formed in situ in molds. Here, the preparation of the polymer by anionic mechanism is preferred. The catalyst systems consist of 0.1-1.0 mole percent of acetyl caprolactam and 0.15-0.5 mole percent sodium caprolactam. The reaction temperature is kept between 140-180 °C. An exotherm can raise it as much as 50 °C as the polymerization proceeds. 

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